The present invention relates generally to mobile radio systems.
Generally speaking, in mobile radio systems, a distinction can be drawn between two types of services, namely circuit-switched mode services and packet-switched mode services. One example of packet-switched mode services is the General Packet Radio Service (GPRS) for Global System for Mobile communications (GSM) mobile radio systems.
The architecture of packet-switched mode systems, for example GSM/GPRS systems, is outlined in FIG. 1, and essentially comprises:                Base Transceiver Stations (BTS) communicating with Mobile Stations (MS) and Base Station Controllers (BSC), the combination of the BTS and the BSC being called the Base Station Subsystem (BSS), or more generally the Access Network (AN); and        entities such as Serving GPRS Support Node (SGSN) entities, communicating on the one hand with the BSS and on the other hand with Gateway GPRS Support Node (GGSN) entities, which in turn communicate with external networks (not shown).        
The interface between the MS and the BSS is called the Um interface and the interface between the BSC and the SGSN is called the Gb interface.
The BSS encompasses functions common to circuit-switched mode services and packet-switched mode services and functions specific to packet-switched mode services; the latter are supported by a particular entity of the BSS called the Packet Control Unit (PCU), not shown specifically in FIG. 1.
For circuit-switched mode services, and as also shown in FIG. 1, the BSS is connected to external networks via an entity called the Mobile-services Switching Center (MSC). The interface between the BSC and the MSC is called the A interface. The combination of the MSC (for circuit-switched mode services) and the SGSN and the GGSN (for packet-switched mode services) is called the Core Network (CN).
In the layered architecture used to describe the above systems, at the Um interface between the MS and the BBS, a distinction is drawn between:                a first layer, called the physical layer, and        a second layer, called the link layer, which is further divided into a plurality of layers, which are, in increasing level order, a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer, and a Logical Link Control (LLC) layer.        
Similarly, at the interface Gb between the BSS and the SGSN, a distinction is drawn between:                a first layer, called the physical layer, and        a second layer, called the link layer, which is further divided into a plurality of layers, which are, in increasing level order, a Frame Relay layer, a BSS GPRS Protocol (BSSGP) layer, and a Logical Link Control (LLC) layer.        
LLC frames are formed in the LLC layer from higher level data units. In LLC frames these data units are called LLC-protocol data units (LLC-PDU).
The LLC-PDU are then segmented in the MAC/RLC layer to form RLC data blocks. The RLC data blocks are then converted in the physical layer to the format required for transmission at the Um interface.
Signaling protocols are also provided, in particular for Radio Resource (RR) management, Mobility Management (MM), Session Management (SM), Logical Link (LL) control, etc.
For a detailed description of the above systems, see the corresponding standards, published by the corresponding standards organizations.
In accordance with the radio resource management protocol, a packet-switched mode mobile station can operate in either:                a packet transfer mode, in which resources are allocated temporarily, when there is actually data to be sent during a call, the resources for a given transmission direction forming a Temporary Block Flow (TBF) for transferring data between the mobile station and the network, or        a packet idle mode, in which no TBF is set up.        
In contrast, the mode in which resources are allocated to a mobile station in circuit-switched mode is called the dedicated mode, and the resources are dedicated resources in the sense that they are allocated to the mobile station for the duration of the call.
When it is switched on, a mobile station is in an idle mode.
Furthermore, the mobility management protocol defines a GPRS Attach procedure which changes a mobile station from the idle mode to a GPRS attached mode, in which it can access GPRS services. The converse GPRS Detach procedure is also defined. A mobile station is in packet-switched mode between the time at which it starts to access GPRS services (by means of the GPRS Attach procedure) and the time at which it ceases to access them (by means of the GPRS Detach procedure).
A mobile station in idle mode that is not GPRS attached communicates with the network by exchanging signaling on Common Control CHannels (CCCH). A mobile station in packet idle mode that is GPRS attached communicates with the network by exchanging signaling on Packet Common Control CHannels (PCCCH), if such channels are provided in the cell concerned, or via the CCCH. A mobile station in the packet transfer mode that is GPRS attached communicates with the network by exchanging signaling over Packet Data CHannels (PDCH).
The PDCH includes a Packet Data Traffic CHannel (PDTCH) and a Packet Associated Control CHannel (PACCH).
The CCCH includes a number of channels, in particular a Paging CHannel (PCH), also referred to herein as a common paging channel. Similarly, the PCCCH includes a number of channels, in particular a Packet Paging CHannel (PPCH). As the present invention is more particularly concerned with paging, the term “common paging channel” is used interchangeably hereinafter for the PCH itself and for the CCCH, and likewise the term “packet paging channel” is used interchangeably for the PPCH itself and for the PCCCH.
For a mobile station supporting both types of service (circuit-switched mode services and packet-switched mode services), either simultaneously or alternately, depending on its capacities, a Circuit Services paging message (CS paging message) is sent to a mobile station in packet idle mode or in packet transfer mode if a circuit-switched mode connection must be set up to the mobile station concerned.
Paging coordination is then advantageously employed, meaning that the network sends circuit-switched mode service paging messages on the same channel as that which is used to send packet-switched mode service paging messages, which is either a GPRS paging channel (i.e. the PCCCH, if present, or the CCCH otherwise) or a GPRS data channel (PDCH), if this kind of channel has been allocated to the mobile station.
The 3G TS 23.060 standard then makes a distinction between the network operating modes summarized below:                Network Operation Mode I (NMO I): the network sends a Circuit-Switched mode service paging message (CS paging message) to a GPRS attached mobile station, either on a GPRS paging channel (i.e. on the PCCCH, if present, or on the CCCH otherwise) or on a GPRS data channel (PDCH), if this kind of channel has been allocated to the mobile station. This means that the mobile station needs to listen to only one of the two paging channels (PCCCH or CCCH) if no other data channel has been allocated to it; if a GPRS data channel has been allocated to it, it receives the paging message on that channel. Thus in this mode coordination is effected by the core network.        Network Operation Mode II (NMO II): the network sends a Circuit-Switched mode service paging message (CS paging message) to a GPRS attached mobile station on the common paging channel (CCCH), which is also the GPRS paging channel (the packet paging channel is not provided in the cell concerned). This means that the mobile station need only listen to the common paging channel (CCCH), but it can listen to this channel even if it has been allocated a GPRS data channel. It is therefore considered that there is no coordination in this operation mode.        Network Operation Mode III (NMO III): the network sends a Circuit-Switched mode service paging message (CS paging message) to a GPRS attached mobile station on the common paging channel (CCCH) and sends a Packet-Switched mode service paging message (PS paging message) on the GPRS paging channel, i.e. either on the packet paging channel (PCCCH), if provided in the cell concerned, or on the common paging channel (CCCH) otherwise. This means that a mobile station in packet idle mode wishing to receive circuit-switched mode service paging messages as well as packet-switched mode service paging messages must listen to both paging channels (the common paging channel and the packet paging channel) if a packet paging channel is provided in the cell concerned. Furthermore, a mobile station in packet transfer mode can also listen to the common paging channel in order not to miss circuit-switched mode service paging messages. Thus no coordination is effected by the network in this mode.The network operation mode is NMO I if an interface called the Gs interface is provided between the MSC and SGSN entities. In this case circuit-switched mode service paging messages originating from the MSC and addressed to a GPRS attached mobile station take a path that passes through the SGSN. This is because, by virtue of the Gs interface, the MSC can tell if a mobile station is GPRS attached. If it is not GPRS attached, the circuit-switched mode service paging message is sent to the BSS via the A interface. If it is GPRS attached, the circuit-switched mode service paging message is sent to the SGSN via the Gs interface and is then forwarded from the SGSN to the PCU entity of the BSS via the Gb interface. The PCU can then send this message on the appropriate channel, that is to say:        the PACCH if the mobile station is in the packet transfer mode, or        the PCCCH if the mobile station is in the packet idle mode and this kind of channel is provided in the cell concerned, or        the CCCH if the mobile station is in the packet idle mode and no PCCCH is provided in the cell concerned.        
However, the presence of the Gs interface imposes a number of constraints. In particular, this involves using new Mobility Management (MM) procedures for packet-switched mode services. This is because, as specified in the 3G TS 23.060 standard, combined circuit/packet MM procedures must then be supported, which could call into question the quality of service for circuit-switched mode services. Moreover, as no system including a Gs interface is yet commercially available, implementation faults cannot be ruled out initially. For these reasons, some operators have stated that they do not intend to deploy any such interface.
A need therefore exists for paging coordination without using this kind of interface, i.e. for paging coordination by the BSS.
The current version of the 3G TS 04.60 standard specifies that paging using the PACCH is applied when a paging message is sent to a mobile station in packet transfer mode that is GPRS attached and if the network is capable of coordinating the paging request with the radio resources allocated to the mobile station on the PDCH. It further specifies that this type of paging coordination must be provided in NMO I (cf. 3G TS 23.060), and that the mobile station must assume that this type of paging coordination is also provided in NMO II and NMO III if the network indicates that it supports the Dual Transfer Mode (DTM) function.
Briefly, the DTM function supports both types of service (circuit-switched mode services and packet-switched mode services) simultaneously, the BSS coordinating the resources necessary for each of these modes. For a detailed description of this function, see the corresponding standards.
Thus the current version of the 3G TS 04.60 standard specifies a particular type of paging coordination (using the PACCH) for NMO II and NMO III (i.e. for operating modes that do not necessitate the presence of the Gs interface), provided that the network supports the DTM function.
However, this kind of solution does not constitute a general solution to the problem of coordination of paging by the BSS.
In particular, this type of coordination is provided only if the DTM function is supported. This is not the case in all equipment.
Furthermore, the applicant has observed that this kind of solution also suffers from the following drawbacks and/or limitations:                In reality, it is not necessary for the DTM function to be supported for the BSS to support paging coordination.        If paging coordination is supported without the DTM function being supported, the mobile station cannot tell this at present, since in the present version of the standard the network merely indicates to the mobile station its operating mode and if the DTM function is supported. This being so, the mobile station could listen to a paging channel when it is in packet transfer mode (in which case a data channel has been allocated to it), with the potential consequence of a loss of MAC/RLC data blocks sent on the data channel and/or Circuit-Switched mode service messages (CS paging messages) that might be sent on the data channel.        If paging coordination is supported, and if the mobile station can tell that this is so, it is still the case that coordination is at present not possible in the case of a mobile station in packet idle mode and a cell in which both types of paging channel (packet paging channel (PCCCH) and common paging channel (CCCH)) are provided. This is because, in this case, the mobile station would have to listen to the PCCCH to receive packet-switched mode service paging messages and to the CCCH to receive circuit-switched mode service paging messages. One solution would be not to provide PCCCH (in addition to CCCH), but this kind of solution is not satisfactory, in particular because it cannot support an increase in packet-switched mode traffic, and because it does not provide the benefit of additional functions available only if PCCCH are provided.        
A need therefore exists to eliminate some or all of the drawbacks previously cited in order to provide an effective solution to the problem of coordination of paging by the BSS (or the access network).